1. Field of the Invention
The present invention relates to liquid crystal display, and more particularly, to a method and apparatus for liquid crystal display wherein a liquid crystal display panel using a 2-dot inversion system. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for minimizing a horizontal flickering noise.
2. Discussion of the Related Art
A liquid crystal display (LCD) controls transmissivity of light in liquid crystal cells on a liquid crystal display panel, thereby displaying an image corresponding to video signals. In order to drive the conventional art liquid crystal cells on the liquid crystal display panel, the LCD includes a liquid crystal display panel driving apparatus as shown in FIG. 1.
The liquid crystal display panel driving apparatus of FIG. 1 includes a data driving integrated circuit chip 12 (D-IC chip) for driving source lines SL1 to SLm on a liquid crystal display panel 10, a gate driving integrated circuit chip 14 (G-IC chip) for driving gate lines GL1 to GLn on the liquid crystal panel 10 and a gate start pulse generator GSP 15 for providing a gate start pulse to the gate driving integrated circuit chip 14. More specifically, the liquid crystal panel 10 includes a liquid crystal cell (LC) positioned at each pixel area divided by the source lines SL1 to SLm and the gate lines GL1 to GLn crossing each other, and a thin film transistor (TFT) positioned at each intersection between the source lines SL1 to SLm and the gate lines GL1 to GLn.
The thin film transistor TFT delivers a data signal on the source line SL into the liquid crystal cell LC when the gate line GL is enabled. Then, the liquid crystal cell LC charges an input data signal, via the thin film transistor TFT, from the source line SL and controls an amount if the transmitted light in accordance with a voltage level of the charged data signal.
In driving such a liquid crystal display, one of the following driving methods may be employed: a line inversion system, a column inversion system, a dot inversion system, a 2-dot inversion system, and a group inversion system.
In the dot inversion system, as shown in FIGS. 2A and 2B, polarities of the data signals applied to the liquid crystal display panel 10 are inverted every gate line GL with respect to the gate line GL on the liquid crystal display panel 10 and every source line SL with respect to the source line SL, and are inverted every frame on a time basis. In other words, in the method of driving a liquid crystal display panel using the dot inversion system, polarities of the data signals applied to the liquid crystal display panel 10 are inverted every source line SL and every gate line GL on the liquid crystal display panel 10, and every frame.
For instance, in the dot inversion system, polarity DSP of the data signal DS applied to the source line SL from the D-IC chip 12 is inverted every horizontal synchronization interval as shown in FIG. 3. Gate signals GS1 to GSn applied to the gate lines GL1 to GLn from the G-IC chip 14 are sequentially enabled for each horizontal synchronization interval. As shown in FIG. 3, pixel signals PS1 to PSn charged in each liquid crystal cell LC is changed into a voltage level of the data signal when the gate signal GS is enabled and thereafter remains at the changed voltage level until the gate signal GS is again enabled. In other words, each liquid crystal cell charges the data signal DL when the gate signal GS is enabled and maintains the charged voltage for one frame interval.
Such a dot-inversion driving method allows the liquid crystal cells to have the same charge condition. The identity of the charge condition can be explained by a pixel voltage charged in the adjacent liquid crystal cells in the vertical direction when the liquid crystal cells LC21 and LC31 positioned at the second and third gate lines GL2 and GL3 crossing the first source line SL1 are charged.
In the odd-numbered frames, as shown in FIG. 2A, the liquid crystal cell LC21 connected to the second gate line GL2 and the first source line SL1 is charged to a negative(−) data signal DS. At this time, the liquid crystal cell LC11 positioned at the upper side of the liquid crystal cell LC21 has a positive(+) voltage, and the liquid crystal cell LC31 positioned at the lower side of the liquid crystal cell LC21 has a positive(+) voltage. Meanwhile, the liquid crystal cell LC31 connected to the third gate line GL3 and the first source line SL1 is charged to a positive(+) data signal DS. The liquid crystal cell LC21 positioned at the upper side of the liquid crystal cell LC31 has a negative(−) voltage, and the liquid crystal cell LC41 positioned at the lower side of the liquid crystal cell LC31 has a negative(−) voltage.
In the even-numbered frames, as shown in FIG. 2B, when the liquid crystal cell LC21 connected to the second gate line GL2 and the first source line SL1 is charged to a positive(+) data signal DS, the liquid crystal cell LC11 positioned at the upper side of the liquid crystal cell LC21 has a negative(−) voltage, and the liquid crystal cell LC31 positioned at the lower side of the liquid crystal cell LC21 has a negative(−) voltage. On the other hand, the liquid crystal cell L31 connected to the third gate line GL3 and the first source line SL1 is charged a negative(−) data signal DS. In this case, the liquid crystal cell LC21 positioned at the upper side of the liquid crystal cell LC31 has a positive(+) voltage and the liquid crystal cell LC41 positioned at the lower side of the liquid crystal cell LC31 has a positive(+) voltage.
Since two liquid crystal cells vertically adjacent to the liquid crystal cell charged in this manner are always charged into voltages having an opposite polarity, all the liquid crystal cells have the same charge condition. Accordingly, a horizontal flicker does not appear at a picture displayed by the method driving the liquid crystal display panel using the dot inversion system.
In the 2-dot inversion system, as shown in FIGS. 4A and 4B, polarities of the data signals applied to the liquid crystal display panel 10 are inverted every two gate lines GL with respect to the gate line GL on the liquid crystal display panel 10 and every source line SL with respect to the source line SL, and are inverted every frame on a time basis. In other words, in a liquid crystal display panel driving method of the 2-dot inversion system, polarities of the data signals applied to the liquid crystal display panel 10 are inverted every source line SL and every two gate lines GL on the liquid crystal display panel 10, and every frame.
For instance, in the 2-dot inversion system, polarity DSP of the data signal DS applied to the source line SL from the D-IC chip 12 is inverted every two horizontal synchronization intervals as shown in FIG. 5. Gate signals GS1 to GSn applied to the gate lines GL1 to GLn from the G-IC chip 14 are sequentially enabled for each horizontal synchronization interval. As shown in FIG. 5, pixel signals PS1 to PSn charged in each liquid crystal cell LC is changed into a voltage level of the data signal when the gate signal GS is enabled and thereafter remains at the changed voltage level until the gate signal GS is again enabled. In other words, each liquid crystal cell is charged to the data signal DS when the gate signal GS is enabled and maintains the charged voltage for one frame interval.
Such a 2-dot inversion driving method allows the odd-numbered liquid crystal cells and the even-numbered liquid crystal cells to have a different charge condition. This phenomenon can be explained by a pixel voltage charged in the liquid crystal cells adjacent in the vertical direction when the liquid crystal cells LC21 and LC31 positioned at the second and
third gate lines GL2 and GL3 crossing the first source line SL1 are charged.
In the odd-numbered frames, as shown in FIG. 4A, the liquid crystal cell LC21 connected to the second gate line GL2 and the first source line SL1 is charged to a positive(+) data signal DS. At this time, a positive(+) voltage has been charged to all of the liquid crystal cells LC11 and LC21. Meanwhile, the liquid crystal cell LC31 connected to the third gate line GL3 and the first source line SL1 is charged to a negative(−) data signal DS. At this time, a negative(−) voltage has been charged to all of the liquid crystal cells LC31 and LC41.
In the even-numbered frames, as shown in FIG. 4B, when the liquid crystal cell LC21 connected to the second gate line GL2 and the first source line SL1 is charged to a negative(−) data signal DS, a negative(−) voltage has been charged to all of the liquid crystal cells LC11 and LC21. On the other hand, the liquid crystal cell L31 connected to the third gate line GL3 and the first source line SL1 is charged to a positive(+) data signal DS. In this case, a positive(+) voltage has been charged to all of the liquid crystal cell LC31 and LC41.
In other words, the odd-numbered liquid crystal cells charge data signals having always the same polarity as voltages charged in two liquid crystal cells adjacent in the vertical direction. On the other hand, the even-numbered liquid crystal cells charge data signals having always the polarity contrary to voltages charged in two liquid crystal cells adjacent in the vertical direction. Accordingly, the odd-numbered liquid crystal cells are charged more slowly than the even-numbered liquid crystal cells.
For this reason, pixel voltages charged in the even-numbered liquid crystal cells fail to arrive at a voltage level of the data signal unlike the voltages charged in the odd-numbered liquid crystal cells. As a result, a picture displayed by the 2-dot inversion driving method generates a horizontal flicker noise.